One method of densely patterning a polycrystalline film containing layer overlying a semiconductor substrate is disclosed for example in JP 2005-268292 A. The method performs RIE (reactive ion etching) with a mixture of hydrogen bromide (HBr) and additive gases such as chlorine gas (Cl2) or oxygen gas (O2). Nitrogen gas (N2) may also be employed as additive gas other than chlorine gas (Cl2) or oxygen gas (O2).
In semiconductor devices primarily configured by logical circuits, there is little variation in pattern density within the chip, thus, little variation is observed in the etching results originating from the variation in pattern density when etched under the above described conditions. However, in semiconductor devices such as NAND flash memory typically configured by a memory cell region having a dense pattern with close-spacing and a peripheral circuit region having a sparse-pattern with wide-spacing, the above described RIE produces varying etching results originating from the variation in pattern density.
More specifically, when etching the densely patterned memory cell region configured at L/S (Line and Space) of 1:1, and the sparsely patterned peripheral circuit region simultaneously, the deposit (reactive product) of silicon bromide (SiBr) causes variation in the etching result in the dense pattern and the sparse pattern. For instance, in the sparsely-patterned region, increased amount of reactive product is deposited in the widely spaced gate structures, resulting in increased width in the lower portion of the gate structures.